1. Field of the Invention
This invention relates to hydrocarbon conversion processes. More particularly, this invention relates to coupling of conversion processes for different feedstocks to produce products that result from cracking molecules in the feedstocks.
2. Prior Art
With decreasing Petroleum based feedstocks, the need to find ways to more efficiently convert both heavy and light crudes is becoming critical. Several methods for converting very heavy feedstocks such as vacuum bottoms and the like containing metal contamants are known. Some of these are disclosed in the following U.S. Pat. Nos. 4,341,624 (1982); 4,347,122 (1982); 4,299,687 (1982); 4,332,673 (1982); and 4,434,044 (1984).
Efforts to couple units capable of efficiently converting different feedstocks have tended to involve transfer of products produced from one unit to another. An example of such a process is disclosed in U.S. Pat. No. 4,436,613 (Mar. 13, 1984) of S. M. Sayles et al. In '613, a two-stage cascade flow fluid catalytic cracking process is disclosed. Product from the low activity side of the two stage process is transferred to the high activity side and a portion of the high activity side catalyst is transferred to the low activity side. The reason given for withdrawing a portion of used catalyst from the high activity side and transfering it to the low activity side was to replenish catalyst on the low activity side. By "high activity" and "low activity" sides of the two stage process is meant the following: The "low activity" side of the process involves contacting a heavy crude containing metal poisons and high Conradson carbon species with a relatively low activity catalyst as compared to the high activity side. The "high activity" side involves contacting a feedstock which has few, if any, catalyst poisons and which is relatively low in Conradson carbon with a high activity cracking catalyst.
Although some of the high activity catalyst is transferred to the low activity side there is no teaching to disclose that this is done only when the equilibrium catalyst from the high activity side has developed a particular characteristic such as disclosed and claimed in the instant invention. Also not disclosed are the advantages that arise from selectively removing equilibrated high activity catalyst and transfering it to a second stage. Finally, not disclosed is a three stage process such as disclosed in the instant invention but rather only a two stage process.
Not disclosed are two unique problems associated with operation of a metals removal system ("MRS"). One involves difficulties associated with transfer of oblong shaped sorbent particles between fluidized bed zones. The other involves the tendency of MRS product vapors on cooling to deposit carbonaceous materials in transfer lines or zones which are quiescent relative to other surrounding areas; for example, around vapor outlet conduits in a cyclone and in quiescent areas of a cyclone between the highly active vortex zone of a cyclone and the more quiescent particulate transfer zone which leads to diplegs used to remove sorbent particulates. Sudden "flaking off" of carbonaceous deposits have been observed to cause dipleg plugging and plugging in other transfer lines.
Not disclosed also are the opportunities for improving product distribution yields in the direction of light cycle oils depending upon varying MAT values and selection of equilibrium catalyst to be transferred among units of a fluid catalytic cracking unit, a reduced crude conversion unit, and an MRS unit.
MAT value is a micro-activity in volume percent conversion as measured by ASTM Test Method Number D-3907-80.
A Conradson carbon test is a standardized method for determining carbon residue formed after evaporation and pyrolysis of a petroleum product. A Conradson carbon determination is intended to provide some indication of the rate of coke-forming tendency of an oil and has been standardized by ASTM method D 189.
Percent by volume or weight of a feedstock is throughout this specification and claims based upon the total volume or weight, respectively, of the feedstock, unless otherwise stated.
Accordingly, it is an object of this invention to improve ease of transfer of MRS sorbents among fluidized bed zones of an MRS unit.
In still another aspect of this invention, it is an object of this invention to lessen the tendency of MRS product vapors to deposit carbonaceous material in transfer lines or zones.
In still another aspect of this invention, it is an object of this invention to improve overall operations of hydrocarbon conversions.